The continuing advances in power electronics and control algorithms are allowing new electrical solutions to be developed for many systems which, in the past, have been dependant on mechanical or hydraulic technologies. As these new systems are developed and integrated with other systems, new requirements and problems are realized which must be addressed. When one of these new systems is integrated into an aerospace application, a subset of the problems concerns the electrical power generating system (EPGS) from which input power is drawn. Input and power feedback characteristics of the new subsystems, if not properly accounted for, could effect other systems which are also coupled to the EPGS.
One such system used in aerospace applications is an electric actuation system. This system typically comprises an electric motor and motor drive used to control an external surface, such as a flap or spoiler, which is driven by external forces, such as the wind. This system exhibits the characteristics of a regenerative load during periods of its operation, and actually generates electric power which is supplied back to the distribution bus. This excess power can result in an over voltage condition, possibly damaging other systems connected to the distribution bus.
The most common approach for handling the power produced by the regenerative load is to dissipate the fed back power, in a controlled manner, in a resistive element somewhere on the distribution bus. Although effective, the weight and cooling requirements of the dissipative element itself, its controller and the power switches used to control the dissipation, as well as the necessity of fault tolerance, make this approach undesirable. The reason for this undesirability is that, in an aircraft application, each additional pound of equipment relates directly to increased fuel burn, reduced range, and increased operating cost. It is a primary concern of airframe manufacturers and electric system designers, therefore, that the EPGS be light weight, fault tolerant, and capable of maintaining the distribution bus voltage within acceptable parameters, even in the presence of regenerative loads.
To address the concern of weight and reliability, many newer electric power generating systems are being designed utilizing switched reluctance machines which, in addition to providing quality electric power to the distribution bus during the generation mode, also integrate the function of providing starting torque to the engine to eliminate the need for a separate starter, thus realizing a significant weight savings. While these machines are capable of operating in both a start and a generate mode (bi-directional mechanical/electrical energy transformation), the control of these machines to date has not provided an adequate solution to the problem of regenerative power loads. While most control algorithms provide adequate bus voltage control during the generate mode of operation, no control algorithm provides for bus voltage control in the presence of a regenerative load whose magnitude is such that a net negative flow of electrical energy is required of the switched reluctance machine.
The instant invention, however, is directed at overcoming these problems by providing and electric power generating system utilizing a high reliability switched reluctance machine and a control therefore which will maintain the distribution bus voltage within acceptable parameters in the presence of both dissipative and regenerative loads, even during operation where the power returned to the distribution bus exceeds that which is required by the dissipative loads.